The present invention relates to variable valve timing apparatuses that are employed in engines. More particularly, the present invention relates to a variable timing apparatus that includes a phase adjustor and a lift adjustor for controlling the valve timing of intake valves and exhaust valves with cams.
Engine variable valve timing apparatuses control the valve timing of intake valves and exhaust valves in accordance with the operating state of the engine. A variable valve timing apparatus generally includes a timing pulley and a sprocket, which synchronously rotate a camshaft with a crankshaft.
Japanese Unexamined Patent Publication No. 9-60508 describes a typical variable timing apparatus, which is represented by FIGS. 18, 19, and 20. The variable valve timing apparatus includes a phase adjustor, or first actuator, arranged on one end of a camshaft 1202. FIG. 18 is a cross-sectional view taken along line 18--18 in FIG. 19, while FIG. 19 is a cross-sectional view taken along line 19--19 in FIG. 18. FIG. 20 is a cross-sectional view taken along line 20--20 in FIG. 19.
A sprocket 1204, which is driven by a crankshaft (not shown), is integrally coupled with a housing 1206. A vane rotor 1208 is arranged in the center of the housing 1206 and secured to the end of the camshaft 1202 to rotate integrally with the camshaft 1202.
Vanes 1210 project outward from the hub of the vane rotor 1208 to contact the inner wall of the housing 1206. Partititions 1212 project inward from the housing 1206 to contact the hub surface of the vane rotor 1208. Cavities 1214 are defined between the partitions 1212. A first pressure chamber 1216 and a second pressure chamber 1218 are defined in each cavity 1214 between each vane 1210 and the partitions 1212.
Hydraulic fluid is delivered to the first and second pressure chambers 1216, 1218 to rotate the vane rotor 1208 relative to the housing 1206. As a result, the rotational phase of the vane rotor 1208 relative to the housing 1206 is adjusted. This, in turn, adjusts the rotational phase of the camshaft 2102 relative to the crankshaft and varies the valve timing of the intake valves or exhaust valves.
The camshaft 1202 has a journal 1224, which is supported by a bearing 1222 formed in a cylinder head of the engine. An oil channel, which is connected with a hydraulic unit 1220, extends through the cylinder head and connects to an oil groove 1226 extending along the peripheral surface of the camshaft journal 1224. The oil groove 1226 is connected to oil conduits 1227, 1228, which extend through the camshaft 1202. The oil conduit 1228 is further connected to oil conduits 1230, 1232, which extend through the vane rotor 1208 and lead into the first pressure chambers 1216. Accordingly, hydraulic fluid is forced from the hydraulic unit 1220 to the first pressure chambers 1216 through the oil channel, the oil groove 1226 and the oil conduits 1227, 1228, 1230, 1232. A further oil channel, which is connected with the hydraulic unit 1220, extends through the cylinder head and connects to an oil groove 1236, which extends along peripheral surface of the journal 1224. The oil groove 1236 is connected to an oil conduit 1238, which extends through the camshaft 1202. The oil conduit 1238 is further connected to oil conduits 1240, 1242, 1244, which extend through the vane rotor 1208 and lead into the second pressure chambers 1218. Accordingly, hydraulic pressure is communicated between the hydraulic unit 1220 and the second pressure chambers 1218 through the oil channel, the oil groove 1236, and the oil conduits 1238, 1240, 1242, 1244.
In addition to the first actuator, a lift adjustor, or second actuator, employed in a variable valve timing apparatus to change the lift amount and timing of intake or exhaust valves with a three-dimensional cam, is also known in the prior art. Japanese Unexamined Patent Publication No. 9-32519 describes a typical second actuator, which is represented by FIG. 21. Three-dimensional cams 1302 are arranged on a camshaft 1304. A timing pulley 1306 is arranged on one end of the camshaft 1304. The timing pulley 1306 is supported such that it slides axially along and rotates integrally with the camshaft 1304. A cylinder 1308 is arranged on one side of the timing pulley 1306. A piston 1310, secured to the end of the camshaft 1304, is fitted into the cylinder 1308. A pressure chamber 1312 is defined between one side of the piston 1310 and the inner wall of the cylinder 1308. A compressed spring 1314 is arranged between the other side of the piston 1310 and the timing pulley 1306. When the pressure in the pressure chamber 1312 is high, the piston 1310 urges the camshaft 304 against the force of the spring 1314 toward the right (as viewed in FIG. 21). When the pressure in the pressure chamber 1312 is low, the spring 1314 pushes the piston 1310 and forces the camshaft 1304 toward the left.
Hydraulic fluid is delivered to the pressure chamber 1312 from an oil control valve 1318 through oil conduits 1322, 1324, which extend through a bearing 1320, oil conduits 1326, 1328, which extend through the camshaft 1304, and an oil conduit 1332, which extends through a bolt 1330. The bolt 1330 fastens the piston 1310 to the camshaft 1304. A microcomputer 1316 controls the oil control valve 1318 to adjust the hydraulic pressure in the pressure chamber 1312 and change the axial position of the camshaft 1304.
Accordingly, the position of contact between each three-dimensional cam 1302 and the associated valve lift mechanism is adjusted to vary the opening duration of a corresponding intake valve or exhaust valve in accordance with the profile of the cam 1302. This varies the valve timing.
When changing the rotational phase of a camshaft relative to a crankshaft with the prior art first actuator to vary the valve timing, the opening and closing timing of the valves are both varied in the same manner. That is, if the opening timing is advanced, the closing timing is advanced accordingly, and if the opening timing is retarded, the closing timing is retarded accordingly. On the other hand, when changing the lift amount of the valves with the prior art second actuator to vary the valve timing, the opening timing and closing timing of the valves vary inversely at the same rate. That is, if the opening timing is retarded by a certain rate, the closing timing is advanced by the same rate, and if the opening timing is advanced by a certain rate, the closing timing is retarded by the same rate. Therefore, the opening and closing timing of the valves cannot be independently varied. This limits the control of the valve timing.
To solve this problem, the first actuator and the second actuator can be arranged together on a camshaft to adjust both the rotational phase of a camshaft relative to a crankshaft and the lift amount of the valves. This would reduce the limitations on the opening and closing timing control.
For example, as shown in FIG. 22, which illustrates an intake camshaft 1402 and an exhaust camshaft 1404, a first actuator 1408 may be arranged on one end of the intake camshaft 1402, and a second actuator 1410 may be arranged on the other end of the intake camshaft 1402. The first actuator 1408 includes a timing sprocket 1406.
However, the structure formed by installing the first actuator 1408 and the second actuator 1410 on the same intake camshaft 1402 results in a longer camshaft 1402. This would also increase the size of the engine and occupy more space in the engine compartment, and space is very limited.